How to make it
For the mayonnaise: In a blender, combine 1⁄4 cup of the olive oil, the egg yolk, lemon juice, and salt. Put the remaining 3⁄4 cup olive oil in a liquid measuring cup with a spout and get ready to meditate! With the blender on low speed, slowly drizzle in the oil in an extremely thin stream—this should take about 5 minutes. Once there is about 1⁄4 cup olive oil remaining in the measuring cup and the mayonnaise in the blender is visibly emulsified (thick and smooth in consistency), you can pick up your pouring speed. (If the final mayonnaise is too thick, thin it out with a little bit of warm water.)
Store in an airtight container in the refrigerator for up to 1 month.
For the corn: Finely grate the zest of the lime and set aside. Cut the lime into wedges and juice as many wedges as you need to yield 1 teaspoon lime juice.
In a lidded jar or airtight container, combine the feta, yogurt, mayonnaise, red pepper flakes, lime zest, and lime juice and stir to mix. Seal the jar and then chill for up to 3 days. Pack the remaining lime wedges in a ziplock bag and chill for up to 3 days.
Fire the grill or campfire to medium-high heat and position the grill grate 2 to 4 inches above the coals.
Place the ears of corn over direct heat and, using tongs, rotate every 2 to 3 minutes until the ears are uniformly charred and the kernels bright yellow, 10 to 12 minutes. For a darker char, drizzle olive oil over the corn so it drips onto the coals and the flames jump up to lick the corn.
Transfer the corn to a serving plate or baking sheet. Shake the feta mixture to reincorporate and then spread evenly over each ear of corn and sprinkle with the cilantro.
Serve immediately with the lime wedges. This is the kind of finger food you just dig in to and get messy—you’ll have cheese on your face and corn in your teeth but it’s so good you’ll be grinning ear to ear.